Context: Human papillomavirus (HPV) vaccine programs may decrease the morbidity and mortality due to cervical cancer seen among women in low-resource countries. However, the 3-dose schedule over a 6-month period is a potential barrier to vaccine introduction in such settings.
Objective: To determine the immunogenicity and reactogenicity of different dosing schedules of quadrivalent HPV vaccine in adolescent girls in Vietnam.
Design, setting, and participants: Open-label, cluster randomized, noninferiority study (conducted between October 2007 and January 2010) assessing 4 schedules of an HPV vaccine delivered in 21 schools to 903 adolescent girls (aged 11-13 years at enrollment) living in northwestern Vietnam.
Intervention: Intramuscular injection of 3 doses of quadrivalent HPV vaccine delivered on a standard dosing schedule (at 0, 2, and 6 months) and 3 alternative dosing schedules (at 0, 3, and 9 months; at 0, 6, and 12 months; or at 0, 12, and 24 months).
Main outcome measures: Serum anti-HPV geometric mean titers (GMT) measured 1 month after the third dose of the HPV vaccine was administered; GMT was determined by type-specific competitive immunoassay. Noninferiority of each alternative vaccination dosing schedule was achieved if the lower bound of the multiplicity-adjusted confidence interval (CI) of the type-specific GMT ratio for HPV-16 and HPV-18 was greater than 0.5 (primary outcome). Safety outcomes were immediate reactions, local reactions, fever within 7 days after each dose, and serious adverse events up to 30 days following the last dose.
Results: In the intention-to-treat analysis, 809 girls who received at least 1 HPV vaccine dose had valid serum measurements 1 month after the third dose. After the third dose, the GMTs for those in the standard schedule group who received doses at 0, 2, and 6 months were 5808.0 (95% CI, 4961.4-6799.0) for HPV-16 and 1729.9 (95% CI, 1504.0-1989.7) for HPV-18; 5368.5 (95% CI, 4632.4-6221.5) and 1502.3 (95% CI, 1302.1-1733.2), respectively, for those whose received doses at 0, 3, and 9 months; 5716.4 (95% CI, 4876.7-6700.6) and 1581.5 (95% CI, 1363.4-1834.6), respectively, for those who received doses at 0, 6, and 12 months; and 3692.5 (95% CI, 3145.3-4334.9) and 1335.7 (95% CI, 1191.6-1497.3), respectively, for those who received doses at 0, 12, and 24 months. Noninferiority criteria were met for the alternative schedule groups that received doses at 0, 3, and 9 months (HPV-16 GMT ratio: 0.92 [95% CI, 0.71-1.20]; HPV-18 GMT ratio: 0.87 [95% CI, 0.68-1.11]) and at 0, 6, and 12 months (HPV-16 GMT ratio: 0.98 [95% CI, 0.75-1.29]; HPV-18 GMT ratio: 0.91 [95% CI, 0.71-1.17]). Prespecified noninferiority criteria were not met for the alternative schedule group that received doses at 0, 12, and 24 months (HPV-16 GMT ratio: 0.64 [95% CI, 0.48-0.84]; HPV-18 GMT ratio: 0.77 [95% CI, 0.62-0.96]). Pain at the injection site was the most common adverse event.
Conclusions: Among adolescent girls in Vietnam, administration of the HPV vaccine on standard and alternative schedules was immunogenic and well tolerated. The use of 2 alternative dosing schedules (at 0, 3, and 9 months and at 0, 6, and 12 months) compared with a standard schedule (at 0, 2, and 6 months) did not result in inferior antibody concentrations.
Trial registration: clinicaltrials.gov Identifier: NCT00524745.